working indicator

Where is the indicator used?:
- on batch update.
- on every attempt to fetch a collection. To see it you would need to set bootstrapped data to false in /public/app/browseWorks.js : 146;
- while saving an edited work
These lines (add class, insert overlay) and the corresponding two below (remove class and overlay) are the same everywhere the progress indicator is used.  They should be moved into functions in util.js to make the code clearer and so that any changes to the overlay presentation later can be done in one single place.